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Methyl orange

Methyl orange



IUPAC name	4-dimethylaminoazobenzene-4'-sulfonic acid sodium salt
Other names	p-dimethylamino-azobenzenesulfonic acid
Identifiers
CAS number	547-58-0
SMILES	CN(C)c1ccc(cc1)N=Nc2ccc(cc2)S(=O)(=O)O[Na]
Properties
Molecular formula	C₁₄H₁₄N₃NaO₃S
Molar mass	327.33 g/mol
Density	1.28 g/cm³, solid
Melting point	>300 °C (Not precisely defined.)
Boiling point	Decomposes.
Solubility in water	Soluble in hot water
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Methyl orange is a pH indicator frequently used in titrations.

Additional recommended knowledge

Essential Laboratory Skills Guide

It is often chosen to be used in titrations because of its clear colour change. Because it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point.

Indicator colours

Methyl orange (pH indicator)
below pH 3.1		above pH 4.4
3.1	↔	4.4

Methyl orange in xylene cyanole solution (pH indicator)
below pH 3.2		above pH 4.2
3.2	↔	4.2

In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity. It should be noted that the entire colour change occurs in acidic conditions.

In an acid it is reddish and in alkali it is yellow.

Other Indicators

Modified (or screened) methyl orange, an indicator consisting of a solution of methyl orange and xylene cyanol, changes from gray to green as the solution becomes more basic.
A number of other common indicators are tabulated in the article on pH indicators.

Category: PH indicators